Code transmission system



March 8, 1938. H. o. RUGH CODE TRANSMI SSION SYSTEM Filed Aug. 14, 1935 fnueni argar) 0. f1 uy/ L Patented Mar. 8, 1938 UNITED STATES PATENT OFFICE 3 Claims.

This invention relates to the coding of messages which are to be transmitted by wire or over the air between two stations for the purpose of maintaining the contents of the message secret. 4

The invention is particularly adapted for use in the transmission of messages electrically by the use of the so-called Baudot method whereby combinations of electrical impulses constitute signals representing certain characters such as the letters of the alphabet.

In my prior application, Serial No. 756,057, filed December 5, 19,34 for Code transmission system, a system is provided whereby a message to the actual transmitting stage and is automatically decoded at the receiving station for which it is intended, leaving other receiving stations toreceive the message in its coded form.

It is the purpose of the present invention to provide a methodof coding and decoding mes-. sages under the control of the transmitter station. In all coding systems utilizing a substituted character for the intended character as in the present case it is possible if the message is intercepted to trace the substitutions owing to the recurrence of certain characters such,.ior example, as the vowels of the alphabet.

This method of deciphering codes depends primarily upon determining the relative frequency withwhich the characters appear in any message;

The present invention provides means whereby the code may be changed so frequently as to make it impossible for anyone to decipher the message by obtaining information as to the frequency of recurrence of any character.

I have illustrated my invention as applied to a transmitting system using a single channel or line between the sending and the receiving station such as is disclosed in the United States patent to Baudot No. 388,244. The sending and receiving machines may be generally of the construction shown schematically in the drawing, that is, ordinary telegraphic transmitting and receiving typewriters or they may be similar to that shown in the Rugh Patent Number 1,937,983.

The purposes and advantages of the invention will appear more clearly as the description proceeds in connection with the accompanying drawing, wherein- The figure is a schematic diagram showing a transmitting station and a receiving station embodying the mechanism necessary to carry out the present invention. 5, Referring now in detail to the drawing, the

be sent is changed or coded before it reaches (Cl. PIS-22) transmitting station is designated generally by the numeral l0 and the receiving station by the numeral II. The transmitting station embodies a source of current I2, a series of keys l3, of which only one is shown, it being understood, of course, that these keys are part of a telegraphic typewriter. Each of the keys I3 is preferably provided with a stepping pawl M which is adapted to rotate a ratchet wheel l5 one step each time the key is depressed to close a pair of contacts l6 and H. The contact I6 is carried by a pivoted arm I8'which has a roller [9 riding on the ratchet wheel i5. In addition, the transmitting instrument embodies a key 20 and a key 2|, the purpose of which will be more fully explained hereinafter. The keys l3, when depressed, are adapted to make contact with certain combinations of stationary contacts of which there are five in number appearing directly under the key I3 and numbered from I to 5. Contacts I to 3 lead to a connecting net work 22 where each lead from the contacts is connected to a stationary contact in each of the three banks 23, 2'4 and 25. It will be noted that the lead from contact I of key i3 is connected to the left hand stationary contact in bank 23 to the middle and right hand stationary contacts of bank 24 and to the right hand stationary contact of bank 25. As shown, contacts 2 and 3 under key l3 are connected to the banks 23, 24 and 25 of stationary contacts in the following manner: The lead from contact 2 connects to the center stationary contact of bank 23, to the left hand stationary contact of bank 24 and has no connection to bank 25. The lead from contact 3 under key I3 connects to the right hand stationary contact of bank 23 and to the left hand and center stationary contacts of bank 25.

A series of wiper arms 26, 21 and 28 are pivoted on a suitable support (not shown) and are also connected to an operating bar 29 which is movable to shift contacts 26, 2'! and 28 in unison from one of the stationary contacts to another of the banks 23, 24 and 25. The contact members 26, 21 and 28 are directly connected to segments i, 2 and 3 of a distributor 30. This distributor is of the well known type including six sections insulated from each other and a wiper arm 3! having a brush 32 adapted to contact the several sections as the arm 3! is rotated. The wiper arm 3! is normally held in stop position by a stop pawl 33 so that it will engage the starting section 6. When contact is made between contacts i6 and I1, current is supplied from battery I? to a relay 34 for withdrawing the stop pawl 33 to permit rotation of the arm 3|. It is understood, of course, that suitable means are provided for rotation of the arm 3| as is well understood in the art. A transmission line 35 connects the arm 3| with an arm 36 of a second distributor 31 at receiving station. The arm 36 has a brush 38 thereon and is also held by a stop pawl 39 similar in all respects to stop pawl 33. Also, when current is supplied to arm 3| from battery |2, the path of the current extends from arm 3| to arm 36, the brush 38 and the stationary contact 36 on the distributor 31 through a relay 46 to ground, to thereby release stop pawl 39 at the same time stop pawl 33 is released. In the normal operation of an electrical transmitting device of this character the depression of a key, such as 3, would result in starting both arms 3| and 36 in motion and at the same time the key depressed would close one or more of the contacts to associated therewith. Assuming that contact is closed by depressing key l3, it will be noted that a circuit is made from battery |2 through key |3, contact and the left hand contact of the stationary bank 23, movable contact 26 and segment I of the distributor 36. Now, when arm 3| contacts the segment I of the distributor 30, the circuit is extended through brush 32, arm 3| and the transmission line 35 to arm 36. Arm 36 has at this time, however, also arrived upon segment I of the distributor 31. The circuit is therefore extended through arm 36 and its brush 38 and segment I to movable contact 4| in a bank of movable contacts 4|, 42 and 43 at the receiving station These contacts at the receiving station are also connected to an operating arm 44 so that they may be moved in unison over the banks 45, 46 and 41 of stationary contacts at the receiving station. Banks of contacts 45, 46 and 41 at the receiving station are connected to a plurality of relays I, 2 and 3 at the receiving station and these relays control suitable arms such as 48 for operating typing keys 49 to imprint a character upon a sheet of paper which may be provided on the roll 50. The details of this mechanism, however, are well known in the art and will not be described herein. The circuit as traced thus far will, of course, be completed to ground at relay to cause the actuation at the receiving station of the key corresponding to key l3 at the transmitting station.

The banks of contacts 45, 46, and 41 at the receiving station are connected to relays I, 2, and 3 in the same manner as the banks of stationary contacts 23, 24, and 25 are connected to the contacts to 3 under the key l3, thus producing a network which is the duplicate oi. the network 22.

In the present method of coding messages, I employ means for actuating the bars 29 and 44 to shift movable contacts 26, 21 and 28 at the transmitting station and movable contacts 4|, 42 and 43 at the receiving station at the will ofthe transmitter so that these movable contacts may be shifted to any desired position on their stationary banks of contacts as frequently as is desired by the transmitter of the messages. In order to accomplish this result, the keys 20 and 2| are provided at the transmitting station and key 20 is adapted to contact a contact 4 beneath it for directly connecting battery l2 to segment 4 upon the distributor 30. The key 20 is also provided with a contact 5| for engaging a stationary contact 52 to connect battery |2 to a relay 53 for energizing this relay. When the relay 53 is energized it attracts a spring held armature 54 which, in turn, operates a pawl 55 movable between a pair of steps 56 and 51 to cause this pawl to a ratchet segment 58, which segment is pivoted at 59 and is connected by link 60 to the bar 29. Thus, when the pawl 55 is moved down, it will move the bar 29 to shift contacts 26, 21 and 28 on to the middle contacts of the respective banks 23, 24 and 25. The keys 26 and 2| are also provided with suitable pawls, like H, to engage corresponding ratchet wheels |5 on the shaft I5 so as to close contacts l6 and I1 when either key is depressed to thus cause the rotation of wiper arms 3| and 36. When the wiper arms 3| and 36 arrive at the fourth segments of their dis tributors, they complete a circuit from battery |2 through key 20 and contact 4 associated therewith, segment 4 and wiper arm 3| of the distributor 30, line 35, arm 36 and segment 4 of distributor 31 to relay number 4 and ground. Relay number 4 controls a stepping arm 6| at the receiving station so that when relay 4 is energized it attracts this arm to close a contact 62 thereon with a contact 63 leading to a relay 64. The relay 64 operates a stepping mechanism consisting of an armature 65 and a pawl 66 engaging a ratchet segment 61 pivoted at 68 to a suitable support not shown. The ratchet segment 61 is connected by a link 69 to the bar 44 so as to control the movement of the movable contacts 4|, 42 and 43. Thus, when the movable contacts 26, 21 and 28 are moved to the middle contacts of their respective banks, the movable contacts 4|, 42 and 43 also are moved to the middle contacts of their respective banks. Relay 64 is energized from a battery l2 at the receiving station.

It is evident from the connection of the contacts 2 and 3 associated with the keys |3 with their respective banks 23, 24 and 25 and the connection of relays of 2 and 3 at the receiving station with their respective banks 45, 46 and 41 of stationary contacts that the impulses transmitted over line 35 will not be the same as when the movable contacts 26, 21 and 28 and 4|, 42 and 43 were on the left hand stationary contacts of their respective banks. Therefore, impulses transmitted for a given key l3 although receivable at the receiving station H to again actuate the same relay, will not do so upon some other receiving station which has not been correspondingly shifted. Thus, the operator at the transmitting station can, by actuation of the key 26, cause changes in the impulses transmitted by the impression of any particular key |3 as often as he desires and corresponding changes will be set up at the receiving station. I have shown only three stationary contacts in each bank at the sending and the receiving stations, although it is evident that there may be any desired number within the limits of the combinations of the five groups of impulses used.

The key 2| is utilized to return the stepping mechanism for the bars 29 and 44 to starting position whenever desired. Thus, this key 2| connects through contact 5 the source of current |2 to segment 5 on the distributor 30 and correspondingly the relay 5 at the receiving station is connected to segment 5 on the distributor 31 to control an arm which, in turn, controls the connection of battery l2 through contacts 1| to a release relay 12. The contacts 13 and 14 associated with the key 2|, control connection of the battery [2 to a release relay 15. When release relays 12 and are energized, they attract the pivoted armatures 16 and 11 associated therewith which pivoted armatures are really holding pawls engaging the ratchet segments 61 and 58 and when these pawls are attracted by their respective relays they also actuate the pawls 55 and 66 by means of the pins 18 and 19 thereon to release these pawls from the segments 58 and 6'! permitting the segments to return to zero or starting position, due to the springs 80 and 8| associated therewith.

From the above description it is believed that the diagrammatic sketch will be sufliciently clear to indicate how the operator at a transmission station l may change the code by which he is transmitting a message as frequently as he desires by manipulation of the step key 20 and the zero or return key 2|. The code will be correspondingly changed at the receiving station although the message sent would, if picked up by someone else from the line 35, be wholly unintelligible. The code changes may be made at definite intervals, that is to say, for every word or for every ten characters or in any manner, the operator sees fit. Hence, no sequence of repetition of characterswould be of any aid in deciphering the message.

I have discovered that the same system may be used by the receiver of a message to decode the message provided he has a duplicate of the apparatus shown in the drawing, that is, a transmitting instrument and a receiving instrument and provided he knows the intervals at which the codes were changed and the changes made. To decode the message in this fashion, it is only necessary for the receiver of the message who has received it without it going through a decoding receiver, such as II, to transmit the message as received in the code on his local transmitter to his local receiver, making the same changes in the code as were made by the transmitter in originally sending the message. If the code change has only been a simple transposition such, for example, as connectingcontact I associated with the key l3 to segment 2 of the transmitting distributor and contact 2 of the key bank with segment I of the distributor, these changes will come correct upon the message being transmitted through the transmitting system one time. 1 The more complicated changes, however, require continued running of the message two or three or more times through the transmitter with the operator continuing to make the same code changes as were made originally when the message was sent. Ultimately, the diiferent groups of the entire message will be decoded until it reads exactly like it was sent by the original operator at the transmitting station.

From the above description it is believed that I the features of the present method of transmitting coded messages will be clear to those skilled in this art and the advantages thereof, readily apparent.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

1. A system for the secret transmission of messages which comprises a sending station, means for translating the characters of a mes sage into combinations of electrical impulses at the sending station, means at the sending station for transposing the order of the impulses in the combinations before transmission thereof, a receiving station having means to receive impulses in the order in which they are transmitted, means at the receiving station for restoring the order of impulses, control means at the sending station for said restoring means, a character selecting means at the receiving station actuated by the impulses after they have passed through said restoring means, said transposing and restoring means comprising duplicate net works at the sending and receiving stations respectively and having banks of stationary contacts connected in multiple to the translating means and the selecting means respectively, and movable contact members movable over the contacts of v said banks by actuation of said control means.

2. In a system of the character described, a sending station, means at the sending station for translating the characters of a message into combinations of electrical impulses, a receiving station having means to receive the impulses in the order in which they are transmitted, character selecting means at the-receiving station actuated by the impulses, and manually operable control means at the sending station for effecting in rapid succession a plurality of different transpositions in the order of impulses in the combinations before transmission thereof, said receiving station having a device for restoring the order of impulses, and said control means being operatively connected to said restoring means whereby to cause said restoring means to be correspondingly changed for each trans position eiiected at the sending station.

3. In a method of secretly transmitting a coded message and decoding the same when received which comprises setting up at a sending station combinations of electrical impulses representing the characters of the message, and transmitting said impulses to a receiving station, and selecting characters at the receiving station by means of the received impulses, those steps in the method which comprise transposing the order of the impulses in the combinations before transmission thereof, continuously and repeatedly changing the order of transposition at the sending station, selecting characters at the receiving station by means of the impulses as received in their transposed order whereby to form a message in code, and thereafter decoding the message at the receiving station by transmitting the 

